GRB 050721A
GCN Circular 3654
Subject
GRB050721A: Swift-BAT detection of a weak burst
Date
2005-07-21T06:04:14Z (20 years ago)
From
Angelo Antonelli at Obs. Astro. di Roma <a.antonelli@mporzio.astro.it>
GRB050721A: Swift-BAT detection of a weak burst
L.A. Antonelli (INAF/OAR), K. Page (U. Leicester), D. Morris (PSU), P.
Romano (INAF/OAB), N. Gehrels (GSFC), P. Roming (PSU), P. Schady
(MSSL), G. Tagliaferri (INAF/OAB) S. Barthelmy (GSFC), H. Krimm
(GSFC/USRA), C. Markwardt (GSFC/UMD), D. Palmer (LANL), on behalf of
the Swift team:
At 04:29:14.28 UT, Swift-BAT triggered and located GRB050721
(trigger=146970). The spacecraft slewed immediately. The BAT on-board
calculated location is RA, Dec 253.445d,-28.390d {+16h 53m 47s,-28d 23'
22"} (J2000), with an uncertainty of 3 arcmin (radius, 90% containment,
stat+sys). The BAT light curve shows a peak with a total duration of
~10 sec. The peak count rate was ~1000 counts/sec (15-350 keV), at ~5
seconds after the trigger.
The XRT started the observation at 04:32:20 UT with XRT in automatic
state, 186 sec after the BAT Trigger. An uncatalogued X-ray source was
detected at the following position RA, Dec 16h 53m 44.7s, -28d 22'
53''.3 with an uncertainty of about 6 arcsec (90% containment). This is
42 arcsec from the BAT position reported above.
Based on the UVOT finding chart there is no new source at the XRT
position.
GCN Circular 3655
Subject
GRB 050721a: Optical Observations
Date
2005-07-21T06:25:56Z (20 years ago)
From
Ken ichi Torii at RIKEN <torii@crab.riken.go.jp>
K. Torii (Osaka U.) reports:
"The error region of the Swift GRB 050721a (Antonelli et al. GCN
3654) was imaged with the 0.3 m telescope in the New Mexico Skies
observatory. The observation started at 2005 July 21, 04:35:23 UT
(369 s after the trigger) and several 120 s integrations in I band
were obtained.
We identify a bright (I~15 mag) fading object whose position is
consistent with the XRT afterglow candidate reported in GCN
3654. However, this source does not seem to be spatially resolved with
a nearby 2MASS star in our frames. Further observations and analyses
are in progress."
GCN Circular 3658
Subject
GRB050721A: optical decay
Date
2005-07-21T08:02:10Z (20 years ago)
From
Paolo D'Avanzo at INAF-OAB <davanzo@merate.mi.astro.it>
P. D'Avanzo, S. Covino, (INAF/OABr), D. Malesani (SISSA), S. Bagnulo, T.
Szeifert (ESO), G. Tagliaferri (INAF/OABr), G. Chincarini (Univ. Milano-
Bicocca), S. Piranomonte, L.A. Antonelli, and L. Stella (INAF/OAR), on
behalf of the MISTICI collaboration, report:
We performed a preliminary analysis on our R-band images (Covino et al.,
GCN 3657) of the field of GRB050721 (Antonelli et al., GCN 3654).
The afterglow indicated by Torii (GCN 3655) and confirmed by Covino et
al. (GCN 3657) faded by ~ 0.9 mag in the R band between July 21.204 UT
and July 21.226 UT (25 and 56 minutes after the GRB respectively). This
implies a decay index of ~ 1.
At our last epoch, the afterglow magnitude was R ~ 18.6, with reference
to USNO star UO600_22128314 assumed to be R = 17.4
This message can be cited.
GCN Circular 3659
Subject
GRB 050721A: Early Swift XRT analysis results
Date
2005-07-21T10:25:27Z (20 years ago)
From
Pat Romano at OAB-Swift <romano@merate.mi.astro.it>
P. Romano (INAF-OAB), L.A. Antonelli (INAF-OAR), G. Chincarini, A.
Moretti, G. Tagliaferri (INAF-OAB), K. Page (U. Leicester), F. Marshall
(GSFC), P. Boyd (GSFC-UMBC) on behalf of the Swift-XRT team:
We have analyzed the Swift XRT data from the first orbit observation of
GRB 050721A (Antonelli et al., GCN 3654). The new refined coordinates are:
RA(J2000) = 16h 53m 44.9s Dec(J2000) = -28 22 51.7
This position is 41 arcseconds from the BAT position given in GCN 3654.
We estimate an uncertainty of 6 arcseconds radius (90% containment).
A preliminary spectral fit (simple absorbed power-law) to the combined
PC and WT data yields a photon index of 1.7+/-0.1 in the [0.5-10] keV
band. The derived NH is 3.16E21 cm^-2, which is higher than the Galactic
value (1.57E21 cm^-2; Dickey & Lockman 1990). The average (194-323
seconds from trigger for WT and 324-463 seconds from trigger for PC)
estimated unabsorbed 0.5-10 keV flux is then 3.5E-10 ergs/s/cm^2.
The light curves in Windowed Timing (WT) and Photon Counting (PC) mode
start 194 and 324 seconds from the BAT trigger (T0), and they show a
fading afterglow with a preliminary decay slope -1.99+/-0.07 (first
orbit only). The unabsorbed 0.5-10.0 keV flux at 1 hour after the burst
is estimated to be 5E-12 ergs/s/cm^2.
GCN Circular 3661
Subject
GRB 050721A: Swift-BAT refined analysis
Date
2005-07-21T16:41:48Z (20 years ago)
From
Hans Krimm at NASA-GSFC <krimm@milkyway.gsfc.nasa.gov>
E. Fenimore (LANL), L. Barbier (GSFC), S. Barthelmy (GSFC),
J. Cummings (GSFC/NRC), N. Gehrels (GSFC), D. Hullinger (UMD),
H. Krimm (GSFC/USRA), C. Markwardt (GSFC/UMD),
T. McMahon (Langston U), T. Mitani (ISAS), D. Palmer (LANL),
A. Parsons (GSFC), T. Sakamoto (GSFC/NRC), G. Sato (ISAS),
M. Suzuki (Saitama), J. Tueller (GSFC), N. White (GSFC),
on behalf of the Swift/BAT team:
At 04:29:14.28 UT Swift-BAT detected GRB 050721 (trigger=146970)
(GCN Circ 3654, A. Antonelli et al.). This burst has been called
GRB 050721A in some circulars, although it is so far the only bona fide
burst of the day. The refined BAT ground position is (RA,Dec) =
253.452, -28.386 {16h 53m 48.5s, -28d 23' 10"} (J2000) +- 3 arcmin
(radius, 90% containment, stat+sys). The partial coding was 13%.
The masked-weighted light curve shows a FRED-like structure with a
single large peak starting to rise at T-5 seconds, peaking at T+3.7 seconds
and decaying back to background levels by T+50 seconds. The peak
is visible in the 15-100 keV energy band, but not at higher energies.
The calculated T90 (15-350 keV) is 39 +- 2 sec (estimated error
including systematics).
The power-law photon index of the time-averaged spectrum is 1.81 +- 0.08.
The fluence in the 15-350 keV band is (5.05 +- 0.25) x 10^-6 erg/cm2.
The 1-sec peak photon flux measured from T+3.7 sec in the 15-350
band is (3.4 +- 0.8) ph/cm2/sec. All the quoted errors are at the 90%
confidence level.